1. Field of the Invention
The present invention relates to a new class of dyes that are only sparingly soluble in water, which are free from sulphonic groups and which carry an aliphatic-carboxylic chain directly bound to the aryl nucleus of the coupling compound. The invention also relates to the use of these dyes in the uniform (levelled) dyeing of polyamide fibers and fabrics.
2. The Prior Art
It is known that with respect to polyamide fibers in particular, it is difficult to obtain dyeings exhibiting excellent uniformity. This is so because of the invariable presence in such fibers of irregularities of a chemical nature (non-homogeneity in the distribution of the basic end groups), or of a physico-chemical or physical nature, such as, for example, the differences in their morphological state, which is more or less crystalline, the differences in the surface structure and in the fiber microporosity, all of which cause variations in the distribution of the dyes in the fiber, and in particular, differences in the behavior of light in relation to diffusion and absorption phenomena. The resulting tinctorial defects are usually called "streakinesses".
Generally, in order to be satisfactory, a dyeing of textile materials should exhibit uniformity and good characteristics of fastness, in particular, fastness to wet treatments.
These two characteristics are not always simultaneously exhibited by a given dye, particularly with regard to the dyeing of polyamide fibers.
In this connection, it can be stated in general, that the faster a dye is to wet treatments, the less satisfactory is its migratory power and, therefore, the less levelling it is on polyamide fibers, and vice-versa.
For dyeing such fibers, dispersed dyes or suitably selected anionic dyes are generally employed.
Dispersed dyes (e.g., Microsetile, ACNA) may be suitably used for preparing light shades, since they possess a high covering power for the fiber irregularities. When preparing medium or full color shades, it is necessary to take into account, in addition to the practical impossibility of obtaining very intense shades with these dyes, their low fastness to wet treatments, as a result of which, these dyeings do not meet the requirements of the various dyed articles. The anionic dyes (e.g. Nailamide, ACNA) offer good possibilities for the preparation of dark color shades, but only scarce possibilities for medium shades while they are generally not at all suited to the preparation of light shades because of their insufficient levelling power. The use of anion-active, cation-active or non-ionorgenic auxiliary agents during the dyeing leads to some improvements with regard to the medium shades, but the obtainment of light and well-levelled shades is almost never possible when using these dyes.